Viscosity index improvers are known in the art. Some of these viscosity index improvers also have dispersant properties and are referred to as dispersant viscosity index improvers.
Viscosity index improvers and/or dispersant viscosity index improvers are typically added to various lubricating oil compositions for purposes inclusive of improving the rheological properties of these compositions, and of improving the performances of the engines in which these compositions will subsequently be used in.
Generally speaking, these viscosity index improvers and/or dispersant viscosity index improvers are polymeric compounds. These polymeric additives can be linear or branched-chained. Alternatively, these polymeric additives may be star-shaped.
It is known in the art that these polymeric additives can be modified to incorporate functional groups which alter its properties. Functional groups which are typically incorporated into these additives include esters, amines, amides, imides, alcohols, sulfides, and nitriles. These functional groups may be either aliphatic or aromatic, branched or unbranched and may be introduced using a variety of methods such as working in solution, either oils or organic solvents, or working in the melt phase. The art indicates that the introduction of similar functionality by different methods can yield different products with unique properties. The skilled artisan will appreciate that a process practiced in solution phase may yield very different products when practiced in the melt phase. Changes in solvent, mass transport (mixing) and compatibility of reagents will alter the product composition, properties, yields and performance.
Although it is generally known that polymeric additives useful as viscosity index improvers and/or dispersant viscosity index improvers can be modified, it is not known which of these modifications will eventually be useful or desirable. For example, not all viscosity index improvers can be modified to have dispersancy properties, nor are all modified viscosity index improvers or dispersant viscosity index improvers useful in similar oil formulations. Thus, while a modified viscosity index improver may be useful in lubricating oil formulations, it may be of no value in the formulation of engine oils. The converse of this illustration is equally true.
As a result of the unpredictable nature of the behavior and utility of modified polymeric additives, it is the accepted wisdom in the art that extrapolations and/or generalization of the properties of one modified polymer to another is inaccurate and misleading. Thus, there continues to exist a need in the art to discover viscosity index improvers or dispersant viscosity index improvers modified or unmodified that have improved rheological properties and good engine performance when used in an oil composition.